A head-up display apparatus (hereinafter referred to as a HUD apparatus) projects an image to a transparent plate member disposed in front of a driver seat (for example, a windshield or a combiner) to provide the driver with various information. In the HUD apparatus, an image is displayed when the image is superimposed to a forward scenery seen through the transparent plate member, and the driver recognizes various information even when the driver is looking at the front.
The HUD apparatus displays an image (a warning image) that warns an approach of an obstacle to a driver who is driving a vehicle, or an image (an alert image) that draws attention (referring to patent literature 1). According to the HUD apparatus, the image is displayed in a field of view of the driver during driving. When the warning image or the alert image is displayed, it is considered that the driver recognizes the image immediately.
The inventor of the present application has found the following regarding the HUD apparatus. In the proposed technique, even when the warning image or the alert image is displayed, the driver may be difficult to be aware of being warned or alerted actually. It is postulated that a HUD apparatus displays an image while being superimposed to a forward scenery. Therefore, even when the warning image or the alert image is displayed, the forward scenery is seen through in the same manner as that when another general image is displayed. Therefore, the driver may be difficult to be aware of the image displayed for warning or alert.